This invention relates to processes for recovering technologically important base metals from domestic and offshore mineral reserves and more particularly to pyroelectrochemical processes for the recovery of these base metals from ocean-based ores.
There is a long-range incentive to develop practical, economically competitive processes for recovering a number of technologically important base metals from domestic and offshore reserves. Cobalt and manganese are two such metals having important uses in alloys, catalysts and other products in the commercial and military sectors. Ocean-floor nodules represent a potentially valuable source of these metals provided effective processes can be developed for their recovery. In general, these nodules contain other metals which are primarily iron, nickel and copper in addition to cobalt and manganese. A typical composition will contain about 30% Mn, 7% Fe, 1% Ni, 1% Cu and 0.3% Co by weight.
A number of processes have been developed to recover or extract certain of the metals from these ores. U.S. Pat. No. 3,901,775; U.S. Pat. No. 3,894,927; U.S. Pat. No. 3,028,233; U.S. Pat. No. 4,144,056; and U.S. Pat. No. 2,425,995 provide disclosures of general interest regarding these processes. In U.S. Pat. No. 3,901,775, a process is disclosed wherein the chlorides of the various metals are formed from the ocean-floor nodules, vaporized and fractionally condensed with the manganese (in the form of manganese chloride) being recovered by a fused salt electrolysis. The vaporized and condensed cobalt salt is subject to leaching and aqueous ion exchange prior to recovery of the cobalt metal by electrolysis. In U.S. Pat. No. 3,894,927, the ore from the ocean-floor nodules is contacted with a molten salt containing alkali halides and alkaline earth metal halides with the individual metal halides being separated from the reaction mixture by various methods which preferably involve the halides being dissolved in an aqueous solution for recovery by ion exchange and aqueous electrolysis techniques. In U.S. Pat. No. 3,028,233, the process involves a by-product dust from steel production wherein the iron is vaporized as a chloride with the manganese chloride being dissolved in an aqueous medium and subsequently treated to recover the manganese. In U.S. Pat. No. 4,144,056, the process involves the use of ferric chloride with an alkaline metal chloride to convert metal oxides in the ore to the chlorides which are then dissolved in an aqueous medium and the metals recovered by electrolysis. U.S. Pat. No. 2,425,995 primarily relates to the recovery of zinc from zinc ore which is treated by heating the ore in the presence of carbon and at a temperature sufficiently elevated to distill off the zinc chloride. Manganese in the ore is converted to chloride and ultimately recovered as manganese oxide. While each of these references is directed to specific techniques for recovering certain metals from various types of ores, they have particular limitations. In some instances, the distillation is carried out at temperatures above 700.degree. C. The distilled metal chlorides are treated by aqueous separation processes, and in some cases the separated metal chlorides are subjected to electrolysis in the molten state to recover the metal.
Accordingly, one object of the invention is the development of a new process for the recovery of metals from low grade ores and particularly ocean-floor nodules. Another object of the invention is the development of a process with reduced dissolution and distillation temperatures. A third object of the invention is the development of a process for direct electrolysis of valued metals from the molten chloridation bath. These and other objects will become apparent from the detailed description below.